1. Field of the Invention
This invention relates generally to the field of thermal printing and specifically to color separation, calibration and control of printer parameters.
2. Description of Background
There are a number of different types of printers commercially available, but not all types are suited to be point-of-sale (POS) printers. POS printers are used to print cash register receipts or credit card charge statements. Full color printing is not required, nor is the ability to print on different types of paper. POS printers tend to be compact so as not to clutter up a cashier's work area.
Many types of POS single color printers are commercially available. Dot matrix printers, thermal printers, and ink jet printers are all used because of their speed and reliability. POS color printers are rare in the marketplace. POS dot matrix color printers require a multi-colored ribbon, which adds to the complexity and size of the printer. Color ink jet printers are unsuitable for POS printers because adding three additional ink jet cartridges for full color (also known as 4-color, i.e., three colors plus black) would add width and complexity to the printer. Color thermal printers are under development, but it is hard to do color graphics on a thermal printer. In addition, special paper is required.
Briefly stated, a 2-color thermal point of sale (POS) printer includes a converter for converting full color printing commands into commands for printing in two colors, a primary color and an alternate color. A three-color image is possible when using the background color of the paper as a color.
Line thermal printers and other types of thermal printers have numerous independently heat-driven thermal elements arranged in line, and print by selectively driving these thermal elements to impart heat to the corresponding position of an oppositely positioned heat sensitive paper, thereby causing the heat sensitive paper to change color. The color produced in the heat sensitive paper by this type of printer differs according to the amount of heat energy imparted by the thermal element. As a result, actual print results, such as the color density, will also differ according to whether or not a selected thermal element was driven immediately before, i.e. whether or not a selected thermal element has residual heat.